Field of the Invention
The present invention relates to relates to a display device, and more particularly to a display device that includes a hard coating layer.
Discussion of the Related Art
Nowadays, the display field has seen a rapid development for visually representing electrical information signals due to the wide spread of information society. A variety of flat panel display devices have been developed with such features as slimness, lightweight and low power consumption. Flat panel display devices have been rapidly replacing the existing cathode ray tubes (CRTs).
Examples of flat panel display devices are liquid crystal display (LCD) devices, organic light emitting display (OLED) devices, electrophoretic display (electric paper display (EPD)) devices, plasma display panel devices (PDPs), field emission display (FED) devices, electroluminescence display devices (ELDs), electro-wetting display (EWD) devices, and so on.
Such a display device typically includes a hard coating film, in order to protect its surface and prevent a glaring phenomenon which is caused by external light irradiated onto its display screen. The hard coating film applied to the related art display device can provide an anti-reflective property. To this end, the hard coating layer according to the related art includes ultra-fine protrusion patterns with a nano size that are obtained by prominently and depressively treating its surface. As such, the hard coating layer can use diffused reflections of the ultra-fine protrusion patterns with the nano-size.
However, manufacture cost for forming nano-sized patterns in the hard coating film is high. Also, an etching process is limited to selected materials, and it is thus difficult to apply the etching process to a variety of materials. Moreover, because the surface of the hard coating film is patterned, it is difficult to form the hard coating film with a high hardness. If the hardness is lowered, it is difficult for the hard coating film to protect the screen of the display device.
The hard coating film according to the related art can be prepared by stacking a plurality of coating layers. The plurality of coating layers can be formed by one of dry and wet methods.
In case of the dry method using vacuum equipment, a hard coating layer is formed on a base film before high and low refractive-index layers are formed with being overlapped with each other several times. A fingerprint resistant coating layer, which has a fingerprint resistant property, can also be formed on the hard coating film already provided with the plurality of coating layers as needed.
When the hard coating film according to the related art is manufactured with the dry method, multiple layer formation processes must be thus performed to form the plurality of coating layers. Due to this, the manufacture cost of the hard coating film largely increases, the manufacture procedure of the hard coating film becomes complicated, and productivity of the hard coating film deteriorates. For example, in order to manufacture the hard coating film according to the related art using the dry method, six layers may be sequentially formed one by one, requiring multiple deposition or coating processes. Due to this, the manufacture procedure for the hard coating film is very complicated, the quantity and size of the base film are limited depending on the used vacuum equipment, and process time is lengthened.
In case of the wet method such as a dip or roll coating method, a hard coating layer and a low refractive-index layer are sequentially formed on a base film. In other words, at least two layers including the hard coating layer must be formed on the base film. Similar to the dry method, a fingerprint resistant coating layer, which has a fingerprint resistant property, can also be formed on the hard coating film already provided with the plurality of coating layers as needed.
The wet method for manufacturing the hard coating film according to the related art relatively may weaken an adhesion force between the low refractive-index layer and the hard coating layer. Also, the low refractive-index layer may have a low hardness due to material properties. In other words, the wet method may make the combination of resin compositions forming the hard coating layer and the low refractive-index layer become poor. As such, the low refractive-index layer and the hard coating layer may be easily separated from each other.